Carat to Gram Converter

Carat to Gram Conversion Explained

The Carat to Gram Converter turns gemstone weights into a unit many people are more familiar with: grams. Carat (ct) is a standardized unit of mass used primarily for diamonds and other gemstones. The modern metric carat is defined as exactly 200 milligrams, which is 0.2 grams. That definition makes conversions predictable and consistent across jewelry, gem labs, and marketplaces.

If you buy or sell gemstones, carat weight matters because it affects value and pricing. If you handle stones operationally—such as inventory, shipping, or appraisal—grams can be useful for packaging and documentation. This tool lets you convert both ways, show milligrams for precision, and run batch conversions when you have multiple stones or a price list.

Key Conversion Formulas

The conversion is straightforward because the carat is defined in metric units:

Because many jewelry contexts use decimals, the converter includes rounding controls to display results at 2, 3, 4, or 6 decimal places. If you need very high precision, using milligrams can help you avoid rounding ambiguity.

Carat vs Karat

A common confusion is carat versus karat. Carat (ct) is a gemstone mass unit. Karat (K) is a gold purity measure. For example, 24K gold is considered pure gold, while 18K gold means 18 parts out of 24 are gold. These units are unrelated, even though they sound similar.

Why Two Stones Can Look Different at the Same Carat Weight

Carat is mass, not size. Two stones can weigh the same but appear different because their density and cut differ. A shallow cut can look larger face-up, while a deeper cut can look smaller even at the same weight. Gem type also matters because different materials have different densities.

Batch Conversion for Lists and Inventory

If you work with multiple stone weights, the batch converter is designed to save time. Paste comma-separated values or one value per line, choose the direction (ct → g or g → ct), and instantly get a table of conversions. The optional CSV export is useful for importing the results into spreadsheets, inventory systems, or pricing tools.

Gold Purity Weight Estimator

Although carats are used for gemstones, many people who search for “carat to gram” are also thinking about jewelry. The purity tab helps you estimate how much of a gold item’s weight is pure gold versus alloy metals. The math is simple:

This feature is a quick estimator for planning and comparison. Actual purity can vary by standards, manufacturing tolerances, and hallmarks, but the calculation provides a clear baseline.

Practical Examples

Conversions are often used in quick checks:

• 1.00 ct equals 0.20 g (200 mg)
• 0.50 ct equals 0.10 g (100 mg)
• 2.50 g equals 12.5 ct

If you price gemstones per carat but need total grams for packaging, these conversions keep your paperwork consistent.

Accuracy, Rounding, and Measurement Notes

This converter uses the exact definition of the metric carat. Differences in real-world use usually come from rounding or from the measuring device rather than the unit definition. For example, two scales may display slightly different values if one is calibrated differently or if it rounds to fewer decimals. When precision matters, use milligrams and keep the same rounding rule across your records.